Hello Mdargin,
please leave the fractional T1 out of the bundle: because MLPPP does not have the capability to handle links with unequal speeds
you should fractionate each T1 in 3 500 kbps logical links in order to bundle them with the fractional T1
no sense doing this, make a bundle of the four T1 and give to the fractional T1 its own IP addressing and an high cost in the protocol in use (OSPF or EIGRP for example).
You can still put some traffic over the fractional T1 using policy based routing (PBR) if desired or simply leave it as a backup
Hope to help
Giuseppe